1. Field of the Invention
The present invention relates to a circuit breaker tripping device. More particularly, the present invention relates to an electromagnetic tripping device for a circuit breaker.
2. Description of Related Technology
A tripping device is a main component part of a circuit breaker and used as an actuator of the circuit breaker which interrupts a circuit by separating a moveable contact piece from a stationary contact piece when the circuit is in abnormal conditions. The circuit breaker used to provide circuit interruption to the circuit and to protect the circuit from ground faults generally employs an electromagnetic tripping device.
The Chinese Utility Model CN2575839Y disclosed a circuit breaker entitled “ground fault circuit breaker having a protection from reverse wiring connection.” The noted circuit breaker employs an electromagnetic tripping device comprising an electromagnetic member for generating electromagnetic force: It also includes an armature mounted slidably within the electromagnetic member and movable under the electromagnetic force and a frame body connected to the armature and moved between a first position and a second position along an axis of the electromagnetic member by driving of the armature. The frame body causes a moveable contact piece to contact with or separate from a stationary contact piece. The circuit breaker also includes a locking member for fixing the armature in the second position. The frame body has a protrusion thereon, in which in the first position, the protrusion engages the movable contact, and in the second position, the frame body pushes the moveable contact piece to contact with the stationary contact piece through the protrusion. The locking member is a permanent magnet which can attract one end of the armature through a magnetic force and contact therewith. The magnetic force of the permanent magnet is used as a retaining force when the ground fault circuit breaker is in a switching on state.
The above conventional electromagnetic tripping device has the following defects. The frame body pushes the moveable contact piece to contact with the stationary contact piece through the protrusion, and an arm of the moveable contact piece needs to have a certain length, thus causing contact between the moveable contact piece and the stationary contact piece unstable and poor. The permanent magnet is used as the locking member for fixing the armature in the second position and the magnetic force of the permanent magnet is used as the retaining force when the ground fault circuit breaker is in a switching on state. The magnet is required to have sufficient magnetic force so as to attract and contact the armature, accordingly, when there is a fault current, the electromagnetic member is also required to have sufficient electromagnetic force so as to move the armature. Thus, when the armature is separated from the permanent magnet and returned to the first position, the moveable contact piece is separated from the stationary contact piece under the elastic force of the moveable contact piece, it tends to cause a tripping failure of the circuit breaker.